DESCRIPTION high resolution magnetic resonance imaging (MRI) to identify the characteristics of carotid bifurcation atherosclerotic plaques and thus predict the clinical course of patients. The proposed studies will determine the sensitivity and specificity of in vivo MRI in the detection of plaque features at the human carotid bifurcation that are linked to plaque instability. High resolution MRI of the carotid artery immediately prior to carotid endarterectomy will allow direct correlation of MR images and histologic features. This in turn will lead to strategies for screening and follow-up of high risk individuals and would allow medical and surgical correction of unstable carotid plaques prior to the development of transient ischemic attacks or stroke. To determine whether MRI can determine if the fibrous cap of an atherosclerotic plaque is intact, different implementations of high resolution black blood imaging techniques will be used to identify and define differences in tissue contrast (including formation of a crater shape) on the luminal plaque surface and these MR images compared with histologic sections (Aim 1). Correlations between fibrous cap rupture, as detected by MRI, and increased ischemic neurologic symptoms, will be determined by the clinical presentation at the time of MR exam (including asymptomatic patients, presumably with less plaque rupture/symptoms), symptomatic status at the time of endarterectomy and histologic features (Aim 2). To determine whether MR images can identify new intraplaque hemorrhage (IH) and organized IH, different implementations of high resolution black blood imaging techniques will be used to identify the contrast features that differentiate IH from other tissues and new from organized IH and by comparison of these MR images with histologic sections (Aim 3). Finally, comparison of the MRI findings to the symptomatic status of the patient, including histology, will determine whether patients with a recent history of ischemic neurologic events show increased evidence of recent IH (Aim 4). A series of 150 surgery patients will be studied during the proposed 5-year studies. All the correlations between the MRI, histology and symptomatic status of each patient will be performed by independent observers, using a double-blind protocol. The accurate diagnosis of fibrous cap rupture and intraplaque hemorrhage/thrombus may have particular clinical relevance since these events are thought to precede and cause thromboembolic occlusion, which in the carotid artery, may result in stroke. These studies may eventually lead to the reliable visualization of the structural characteristics of advance lesions of carotid artery atherosclerosis in vivo which may provide a noninvasive mechanism to detect lesions that may place individuals at greater risk for stroke.